The present invention relates to the field of electrophotographic reproduction and, more particularly, to dual layer organic photoconductive elements such as belts, drums, webs, or the like, which are used in machines such as copying machines. Reference is made to U.S. Pat. Nos. 3,615,415, 3,824,099 and 4,150,987 for their discussion of the general field of the present invention and for their disclosure of some of the specific materials and procedures over which the present invention represents an improvement.
Aforementioned U.S. Pat. Nos. 3,824,099 and 4,150,987 relate to dual layer organic photoconductive elements comprising a conductive substrate such as a paper, metallized plastic film or metal plate, supporting two basic layers, namely a charge generating layer and a charge transport layer. Either layer may be adjacent the conductive substrate, and an adhesive bonding layer may be applied to bond the charge generating layer to the electroconductive support.
During use, the photoconductive element is charged, exposed to light passed through or reflected by the lighttransmissive areas of an imaged original sheet to conduct away the charge in the exposed areas, and the charge retaining or unexposed areas are either "inked" with toner which is transferred to a copy sheet or are first transferred to a copy sheet and then "inked" with toner thereon. The toner is fused on the copy sheet to form fixed images corresponding to the images present on the original sheet.
Dual layer organic photoconductive elements were developed in order to provide extremely fast response to light exposure within the visible range of the spectrum. Preferred materials in this respect are diane blue dyes as the charge generating organic chemicals of the charge generating layer and the p-type hydrazones or triaryl pyrazolines as the organic chemicals in the charge transport layer.
Diane blue dyes have the general moiety structure as follows: ##STR1## . . . wherein Z is a substituent group on the phenyl ring. Preferably, Z is selected from a group consisting essentially of hydrogen, alkyl, alkoxy and chlorine groups, more preferably hydrogen, methyl, methoxy and chlorine groups; and most preferably a chlorine group. Z is preferably attached to the ring in the 2 or 6 position. The most preferred diane blue, Chlorodiane Blue, has chlorine as the Z group in the 2 position.
Chlorodiane Blue is a preferred charge generating material because it has good stability and provides photoconductive elements having a desired shelf life or duration of storage prior to breakdown and deterioration or loss of its charge generating properties. Chlorodiane Blue also has superior light sensitivity and charge generating properties over a broad portion of the visible light range, i.e., between about 400 m.mu. and 700 m.mu.. However, Chlorodiane Blue lacks adequate light sensitivity in the near-infrared range, i.e., between about 680 m.mu. and 1150 m.mu..
Furthermore, charge generating layers based upon Chlorodiane Blue dye or other known charge generating organic chemicals are thin layers which contain the dye in solid particulate form and which therefore are relatively brittle and have low cohesive and adhesive strength.
Various dual layer organic photoconductive elements were also developed in order to provide extremely fast response to light exposure within the near infrared range of the spectrum. For example, it is known that certain organic pigments are sensitive to near IR radiation when they are used as charge generating material in a dual layer organic photoreceptor. These pigments include, for example, squarylium dye (or squaric acid methine dye), metal phthlocyanine such as copper phthlocyanine, and cyanine dyes. However, when these pigments are used in the charge generating layer separately or in a mixed form, photoreceptors thereby prepared exhibit problems with regard to being able to be charged up to a desired surface charge acceptance level. A photoreceptor having this type of problem is basically useless.
In order to provide a bond between the charge generating layer and the conductive support, e.g., commonly a metallized plastic film such as aluminized polyester available from the duPont Company under the trademark Mylar, it is known from Example 6F of U.S. Pat. No. 4,150,987 to apply a bonding layer of a polycarbonate to the conductive support. U.S. Pat. No. 4,150,987 also discloses that polymeric resins, such as polycarbonate resins, can be used as a binder for the charge transport layer, and the fact that other known constituents may be included in the charge transport layer for enhanced adhesion.
We have discovered that known organic photoconductive elements, such as the elements described in the example given above, are still susceptible to delamination and having the problem of brittleness, especially after long term storage, whereby the adhesion between the charge generating layer and the electroconductive support becomes relatively easy to break down and the charge generating layer and charge transport layer also become relatively easy to peel or flake from the support to render the electro-conductive element less desirable for its intended purpose.
Solutions to the brittleness type of problems are described in commonly assigned and copending U.S. patent application Nos. 214,362, filed Dec. 8, 1980, for "Photosensitive Elements and Process" by Chang et al, and 296,667, filed Aug. 26, 1981 for "Photosensitive Elements and Process" by Chang et al. Organic photoreceptors which are stable and sensitive over a broad range of the spectrum, including the near infrared band, are described in commonly assigned and copending U.S. patent application Nos. 214,320, filed Dec. 8, 1980, for "Photosensitive Elements and Process" by Chang et al and 218,389, filed Dec. 19, 1980 for "Photosensitive Elements and Process" by Chang et al.